Parental Care in the Sagebrush Vole (Lemmiscus curtatus)

Abstract

Patterns of parental care have been investigated in several species of voles within the genus Microtus that seem to have different types of social organization (Gruder-Adams and Getz, 1985; Hartung and Dewsbury, 1979; McGuire and Novak, 1984, 1986; Oliveras and Novak, 1986; Thomas and Birney, 1979; Wilson, 1982). In presumably monogamous species such as M. ochrogaster and M. pinetorum, a male and female share a nest and males display paternal care. This pattern of nesting and parental care has been observed under all experimental conditions. In seemingly promiscuous species such as M. montanus and M. pennsylvanicus, males nest separately and exhibit no paternal behavior when observed in large enclosures. In small cages, however, M. montanus and M. pennsylvanicus males display appreciable paternal behavior, though the amount of care is still less than that provided by males of monogamous species under identical conditions. Little is known about parental behavior or social organization within the genus Lagurus. The North American form curtatus (subgenus Lemmiscus; Thomas, 1912) differs from Old World species Lagurus lagurus and L. luteus in several morphological features (Carleton, 1981; Davis, 1939) and recent classifications elevated Lemmiscus to generic status (Carleton and Musser, 1984). Field and laboratory observations of Lemmiscus curtatus provide limited and conflicting information on social behavior. James and Booth (1954) reported that captive male sagebrush voles were excluded from nests of females and killed pups if nests could not be defended. Maser et al. (1974) observed captive females to share nests and to nurse each other's young. Although L. curtatus was described as colonial on the basis of early field studies (James and Booth, 1954; Maser et al., 1974), a recent study indicated that sagebrush voles are solitary or live in pairs (Mullican and Keller, 1986). Given the conflicting results of previous observations on behavior and social organization, the present study was undertaken to record parental behavior in sagebrush voles. We observed seven pairs of voles in a seminatural laboratory environment in which the male could nest either separately or with the female and pups. Patterns of care displayed by Lemmiscus are compared with those of Microtus species recorded under similar conditions in previous studies (McGuire and Novak, 1984, 1986). Animals used in this study were laboratory-reared descendants of stock originally captured in Utah in 1981. All seven pairs had reared at least one previous litter to weaning. Before their use in this study, breeding pairs were housed in 25by 45-cm plastic cages containing a peat and wood-chip substrate and an 8-cm thick layer of straw. Sunflower seeds, oats, cracked corn, Purina rabbit chow, and water were provided ad lib.; a reversed 15L:9D light cycle was maintained. A breeding pair was placed in an observation pen when the female was nearing parturition, as determined by date of birth of the last litter and abdominal palpation. Immediately before introduction of a pair into a pen, the ventral fur of the male was dyed black with Nyanzol D for identification purposes. Generally, breeding pairs spent 3-7 days in the pen before birth of their young. Pens measured 1.3 by 2.6 m; the sides of each pen were lined with sheets of aluminum, and the bottom consisted of a sheet of transparent Plexiglas. Each pen contained a 3-cm-thick substrate of wood chips over which straw was scattered. To provide the opportunity for separate nesting by the adults, pens were divided into three sections with 20-cm-high wooden partitions; openings (3-cm diameter) in partitions allowed voles to move between sections. Pens were suspended 60 cm above the floor so that activities of voles could be observed from below (like other species of voles, sagebrush voles kept the bottom of their nests clear of wood chips). Food and photoperiod were identical to those described for the breeding colony. Data collection began with birth of a litter and continued for 25 days. There were two 45-min observation periods per day. Most observations were conducted between 0800 and 1400 h (lights off: 1100 h) and between 1800 and 2200 h (lights on: 2000 h) because sagebrush voles are crepuscular (Maser et al., 1974).